Grazing Incidence Interferometer


  Why Grazing Incidence?

  Fizeau Interferometers

  Infrared Interferometers

  Dual Wavelength 

  How Phase works



This is the 4-inch aoperture LAZER GRAZER -- notice the open top for easy accessThe Model 4GRP LAZER GRAZER is a non-contacting Grazing Incidence Interferometer. . . the first modestly priced Interferometer for measuring flatness of semi-matte or matte-finished surfaces. The Model 4GRP also permits the measurement of parts which are much larger than its 4-inch aperture because is measures flatness across a 4 inch by 16 inch elliptical beam path as illustrated below.

Principle of Operation
When a rough surface is examined at a low grazing angle, it appears to be highly reflective. The LAZER GRAZER utilizes this principle to produce high contrast interferograms of unpolished surfaces.  A grazing angle of 14.48 degrees was selected since at that angle, each interference fringe equals one wavelength.  With a normal incidence Fizeau Interferometer, each fringe equals one half wavelength. Clicking on the link at the left will provide further information on the subject of Grazing Incidence Interferometers.

Model 4GRP Phase-Shifting LAZER GRAZER
Although, in a double-pass grazing system we trade-off some sensitivity for the capability 
of measuring unpolished parts, one wavelength per fringe is usually more than adequate sensitivity  for such samples. 

If you don't need the 4-inch aperture of the Model 4GRP, please look at our Model 2GRP and 2GRP. The principle is the same... the size and the price are different.

Our 4-inch aperture LAZER GRAZER, Model 4GRP Interferometer operates under the control of Durango Interferometry Software which provides a live interferogram on the computer monitor.  The user can select from a rich palette of graphics, text files and reports.  For further Information click on Durango.

Typical Durango Screen, shown below, showing live interferogram, histogram, and OPD plot. Durango permits the user to select from a wide array of graphics, text files and customized reports.

A typical LAZER GRAZER screen as produced by Durango Software.Note that the live image shows interference fringes on the surface of the test sample while providing a 3-D image of the part. 

This unique display is a feature available only with Graham's Grazing Incidence Interferometers!  This capability is of enormous value in the interpretation of test pieces with complex geometry.

Measure flatness 
                   ...before polishing!
The ability to measure flatness of unpolished parts opens the door to examining surfaces which would be difficult if not impossible for a normal incidence interferometer.  This permits the operator to check parts for flatness while still in the grinding stage. For some operations, this is all that is needed since the finished parts do not require polishing. GRAHAM's LAZER GRAZER  puts an end to all of those “tricks” using wax and china markers to increase reflectivity of the surface.

Difficult substrates easily tested
With the LAZER GRAZER, matte, semi-matte, or polished surfaces can be checked for flatness of virtually any material. Very difficult substrates such as ceramics, graphite, tungsten carbide and silicon carbide can be evaluated with ease.  Even machined metal surfaces can be tested.  The high contrast fringes produced by Lazer GRAZER will assist in fine-tuning the production process and increasing both quality and through-put. 
Comparing the interferogram of a normal incidence Fizeau with a Grazing Incidence FizeauComparison of Normal Incidence 
and Grazing Incidence Interferograms
The Upper drawing shows the interferogram of a part using a normal incidence interferometer.  The interferogram shows 8 fringes. 

With a normal incidence Fizeau interferometer, 
2 fringes = 1 wave. This part is therefore shown to be either concave or convex by:  8 fringes = 4 waves = 2.53 microns

The Lower drawing shows the interferogram of the same part using a grazing incidence Fizeau interferometer. 

With a grazing angle of 14.48 degrees, 1 fringe = 1 wave.  The grazing incidence interferogram shows that the part is either concave or convex by: 4 fringes = 4 waves = 2.53 microns

Because of the wide variation in sample thickness encountered, it is essential to make provision for the sample surface to be totally covered by the incident laser beam. By providing a height adjustment for the tilt table, samples of various thickness can be examined.  After the appropriate tip-tilt adjustment has been made, the tilt-table may be raised or lowered as required for the sample to fully encounter the beam.
Field of View covered by the 2-inch Lazer GrazerBecause of the low grazing angle of the incident light, the illuminated area of the tilt-table is much elongated with the result that a long ellipse of light, in this case 4 times the interferometer's aperture is available for evaluating  long narrow parts.  It can also be used to look at parts substantially larger than the interferometer's aperture by examining a narrow swath across the substrate and then rotating the sample to look at another swath.

Non-contacting Grazing Incidence Interferometers like the 4GRP series of instruments open the door for the flatness measurement of semi-matte and matte finished surfaces -- surfaces which otherwise are not reflective enough to evaluate with an interferometer.

The Model 4GRP Phaseshifting LAZER GRAZER is available now.  This turnkey system is complete with 2.41GHz All-inOne Computer with a 19.45 inch diagonal screen., data acquisition board, phase-shift, and Durango Interferometry Software.

Grazing Incidence Interferometer Measures matte, semi-matte, and polished surfaces
Rugged Construction For high stability even in vibration areas
4-inch aperture (101.6 mm) Measures a 4-inch swath across a 16-inch test piece
1/20 wave fused silica reference surface High accuracy
Single Mode Diode Laser source  Dithered for Sharp, speckle-free images
No video monitor required Live interferogram on computer monitor
Remote control Focus, Zoom, Iris, Intensity, Mode  <ALIGN> <VIEW>
Sturdy Integral Tip/Tilt Table Fine adjustment for easy adjustment
Adjustable height to accommodate thick samples
Two Spot Alignment For easy alignment of Tip/Tilt
EndoPhazeTM Phase Shifting For smooth hysteresis-free phase shifting
CCD Camera  Selected for highest resolution and maximum data capture at minimum cost
Durango Universal Interferometry Software For high repeatability
For high reproducibility
For high speed data reduction
For excellent colorful graphics
2.41 GHz All-inOne computer with 19.45 inch diagonal screen Durango Software, Image Acquisition Board, Data Acquisition Board all installed and configured for the Model 4GRP
Power Requirements  117 Volts 60 Hz or 240 Volts 50 Hz
Small Footprint Lower cost than competitive technology
Semi-Customized Choice of wavelength and CCD camera resolution
4GRP 635 nm  (Visible)
768 x 484 pixels
Polished to Semi-matte
2GRP850 850 nm  (NIR)
768 x 494 pixels
Semi-matte to Matte
2GRP1550 1550 nm  (SWIR)
320 x 256 pixels
Other Wavelengths and Camera resolutions available.  Please enquire
To learn how Grazing Incidence works as well as more about our LAZER GRAZER Interferometers click on  WHY GRAZING INCIDENCE?

Durango and Universal Interferometry Software are Trademarks of Diffraction International.  Visit their website where you can download a FREE Demonstration copy of Durango Interferometry Software.

For Further Information, Prices, Delivery, call Gordon Graham today at 
(818) 700-1263 or send an email to:
Graham Optical Systems,  9530 Topanga Canyon Blvd.,  Chatsworth, CA 91311   Phone (818) 700-1263 
Copyright © 2014 Graham Optical Systems  All Rights Reserved
*Durango is a trademark of Diffraction International 
EndoPhazeTM is a trademark of Graham Optical Systems         This page last  updated April 7, 2014